The project is to include the following parts: 1. Attempts to complete the entire life cycle of Trypansoma brucei in vitro. The remaining part of the cycle is the initiation of pleomorphic bloodstream-form-population cultures with metacyclic forms produced in the tsetse tissue culture system. Extending these studies to Trypanosoma congolense is also contemplated. 2. Continuation of experiments aimed at localization and physico-chemical characterization of the nonvariant antigen (s) limited to bloodstream forms of T. brucei. The search for a possible immunoprotective potential of this antigen is also to continue. 3. Further analyses of VSAs of the fly-transmitted stocks obtained at the Walter Reed Army Institute for Research as well as collection and analyses of additional material obtained in the Amherst laboratories. 4. Using the in vitro system for cultivation of bloodstream forms, to study by capping and other immunologic and chemical means the nature of stimuli for antigenic variation. 5. Initiation of monoclonal antibody investigations with regard to VSAs and other antigens in T. brucei bloodstreams forms. 6. Further comparisons of biologic and antigenic properties of L. donovani strains and substrains grown as promastigotes at 28 degrees C and of substrains of this species adapted to growth as promastigotes at 37 degrees C.